Means for control of light



April 8, 1944. A. L. MAYER ET AL MEANS FOR CONTROL OF LIGHT Filed Nov.14, 1940 FIG.3

INVENTORS ALVIN L. MAYER BY HANS R. KOSSMAN 7 Q 1 ATTZJI SZS L PatentedApr. 18, 1944 MEANS FOR CONTROL'OF LIGHT Alvin L. Mayer, Cincinnati,Ohio, and Hans R. Kossman, New York, N. Y.; said Kossman assignor tosaid Mayer Application November 14, 1940, Serial No. 365,678 4 Claims.ici. 88-24) This invention relates to novel methods and means foraccurately controlling the intensity of light.

One object of the present invention is to provide methods and means forsimplifying the reading of light sensitive devices, such as exposuremeters, and the like, by establishing a zero or base setting relative towhich all readings are taken.

Another object of the present invention is to provide methods and meansfor permitting the intensity of a projected beam of light to beaccurately forecast and predetermined, prior to the actual projectionthereof, in those instances where the intensity of light rays from asubstantially' constant source of illumination are adapted to bemodified by means interposed intermediate the source of illumination andthe locus of the projection lens.

Another object of the present invention is to provide means of thecharacter hereinabove described which may, by way of example, beassociated with photographic printing machines, and the like, for makingit possible and commercially practical to resort to a constant or fixedexposure time in the printing of a plurality of negatives, regardless oftheir relative densities, by accurately controlling and standardizingthe intensity of the projected image bearing beam.

Another object of the present invention is to provide means of thecharacter hereinabove described which may, when associated with photographic printing machines, permit the use of but one grade of sensitizedphotographic printing paper in printing all printable negatives,regardless of their individual densities, by standardizing the intensityof the projected image bearing beam.

Still another object of the invention is to provide means of thecharacter stated, wherein certain variable factors, which wereheretofore under the personal-judgment of an individual operator, are sointerrelated as to effectively reduce the human-judgment-element to aminimum, thereby reducing waste and increasing the quantity and qualityof the final product.

A further object of the invention is to provide means for controllingthe intensity of'a beam of projected light by selectively synchronizingor controlling the aperture size of the projection lens, relative to theintensity of the beam prior to projection, thereby permitting a constantsource of illumination to be employed.

Still a further object of the invention is to.

provide means of the character stated which are inexpensive, fool-proofand durable, yet extremely accurate.

These and other objects are attained by the means described herein anddisclosed in the accompanying drawing in which:

Fig. 1 is a vertical sectional view showing the means of the presentinvention operatively associated with a photographic enlarging andprinting machine.

Fig. 2 is a sectional view on line 2-2 of Fig. 1.

Fig. 3 is a partial vertical sectional view of a photographic enlargingand printing machine showing a modified form of the light control means,comprising the present invention, associated therewith.

Fig. 4 is a plan view of an exposure meter embodying the teachings ofthe present invention.

Fig. 5 is a partial vertical sectional view of the device of Fig. 4showing certain structural details of the device.

At the outset it should be clearly understood that while the controlmeans comprising the present invention are shown associated with acommercial photographic enlarging and printing machine in Figs. 1-3,inclusive, and with a commercial exposure meter in Figs. 4 and 5, suchassociations are exemplary in nature, rather than restrictive.

As shown in Fig. l the device comprising the present invention isassociated with the standard photographic enlarging and printingmachine, denoted generally by the numeral ID, for permitting a lightbeam of constant, predetermined, or standard intensity to be projectedonto the sensitized photographic printing paper II, thereby making itpractical to employ a constant exposure time or shutter speed regardlessof the density of the particular negative being printed.

Machine to may comprise a constant source of illumination such as lamp I2 for projecting the images of photographic negatives placed laterallyin film gate l3 through projection lens I4 onto the sensitized paper itsupported on paper support H0, as well known to the art.

A housing denoted generally by the numeral l5, may be provided betweenthe film gate and the projection lens for confining the beams of light,as is the general practice.

The periods of time during which a beam of image bearing light isprojected onto the sensitized printing paper I! may be controlled bymeans of any suitable shutter element or mechanism denoted generally bythe numeral I6. For the purpose of the present invention, the speedofshutter mechanism I5 may be constant or fixed, since it i proposed to soregulate or standardize the intensity of the image bearing projectedbeam as to make it possible, and commercially practical, to use aconstant exposure printing time as well as but one type or grade ofsensitized printing paper I I for all printable negatives, regardless oftheir individual densities.

It should be clearly understood that the amount, quantity or intensityof light within housing I5 is dependent upon, first, the intensity oflamp I2 and secondly, the relative density or opacity of a negativev orother light modifying means placed within film gate I3. Therefore, it isobvious that if lamp I2 be maintained at a uniform or constantintensity, the intensity of the lesser density than the densestprintable negative are placed in gate I3. In this manner the in-'tensity of the projected image bearing beam for each negative may bestandardized relative to. the predetermined intensity of the so-calledstandard projection beam; after being thus standardized the imagebearing beam may be projected onto the sensitized paper II for theconstant, predetermined exposure time without impairing the quality ofthe finished print.

Such aperture size control means may comprise a diaphragm which may, ifdesired, be in the I form of plate 2I, see Fig. 2, the lower end oflight within housing I5 will be dependent solely upon, and a functionof, the density of the negative, or other light modifying means, placedin gate I3, and through which the light from lamp l2 passes en route tothe projection lens I l. The negative placed in gate I3 may, therefore,be said to modify the normal beam or intensity of light from lamp I2.Inasmuch as the density of each active or light sensitive surfaceexposed to the refiected light within said housing. Light sensitive cellI! may be wired to a suitable current measuring instrument or meter I3by means of conductors M) and El in order that the intensity of whichmay be carried by and secured to a rock shaft 22 in such a manner as tocause the upper apertured portion 45 of plate 2I to progressively reducethe effective aperture of the projection lens III as said plate is swungto the right, about the axis of shaft 22.

In the preferred embodiment of the invention diaphragm may be disposedbetween projection 'lens It and the shutter mechanism I6.

It should be understood that if desired, an iris diaphragm, or any othertype, may be. used to the light within housing I5 may be translated intoa definite swing or deflection of pointer I9 of meter I8. It should beunderstood that the greater the intensity of light within housing I5,the greater will be the swing of pointer I 9, thereby indicating to anoperator the intensity of the normal beam from lamp I2 as modified by anegative placed in gate I3.

In order to facilitate maintaining the intensity of the projection beamat a constant, predetermined value as the intensity of light withinhousing I5 is promiscuously modified by the various negatives placed ingate I3, a zero or base point is established on meter dial I8 relativeto which the intensity of the projection beam for each negative iscompared and standardized.

In the preferred embodiment of the invention the zero or base point isestablished at that deflection or setting of pointer III whichcorresponds to the light condition existing within housing I5 when thedensest printable negative is mounted Using'saidjero point as a base,means are .provided for selectively reducing or controllingtheieffective aperture size of the projection lens ."I {as the intensityof illumination within housing I5 is increased, as occurs when negativesof a selectively control the aperture of len I4 in lieu of the apertureplate 2I disclosed in Figs. 1 and 2. It should likewise be understoodthat if desired, a suitable shutter mechanism and diaphragm may becombined and mounted on projection lens It as is the case in the betterportable cameras, and the like.

The principle of operation of the device of Fig. 1 is as follows: Theactual intensity of the modified light rays within housing I5 will beindicated on meter I8 during those periods of time when the entireactive surface of the light sensitive cell I1 is exposed. If the meterreading is of a value greater than the predetermined zero point, it isobvious that excessive exposure will result unless the intensity of theprojected beam is first reduced to correspond with the intensity of thestandard projected image bearing beam.

In order to accurately predict and preselect the intensity of the beamof projected light prior to the actual projection thereof, means areprovided for selectively controlling, such as, by way of example, bymasking, the active surface of the light sensitive cell II for thepurpose of creating or simulating a light condition at the activelight-sensitive-surface of said cell which corresponds to the lightcondition originally existing within housing I5 when the established onmeter I8.

If desired, a. mask 23 may be mounted for movement relative to theactive surface of the light sensitive cell. If desired, mask 23 may bemounted to reciprocate on a vertical axis relative to cell II, and asillustrated in Fig. 2, said mask may be secured to and carried by theupper end of an actuator rod 24. The lower end of rod 24 may terminatein a follower member 25 which normally engages the upper surface. 26 ofan element 21 which may be suitably secured to rock shaft 22, as shown.A spring such as I24 may be interposed between the lower surface ofhousing I5 and a stop member I25 carried by rod 24 for the purpose ofnormally urging mask 23 downwardly, that is, away from the activesurface of cell I'l. Shaft 22 may be provided with a handle 28, or thelike, to facilitate actuation of said shaft about its longitudinal axiswithin bearings 29.

As clearly discernible from Fig. 2, a clockwise movement of handle 23rotates rock shaft 22 and lifts mask 23 upwardly over the active face ofzero point was the light sensitive cell l1, and, simultaneouslytherewith, diaphragm plate 2| is swung relative to and across theoptical axis of lens i3 thereby reducing the effective aperture of saidlens.

From the foregoing it is apparent that in order to bring pointer 9 toregister with the preselected zero point of meter I8, it is onlynecessary to so manipulate rock shaft 22 as to mask out suiiicientportions of the active surface of the light sensitive cell as tosimulate at the active light sensitive surface of said cell a zero pointlight condition. During this adjustment, diaphragm plate 2! will beshifted relative to lens M for changing the size of the eifectiveaperture of the projection lens in an inverse ratio to the amount oflight being passed by the particular negative mounted in gate ilwherebyto limit the actual intensity of the projected beam to that of thepredetermined standard.

It will be observed that by reason of the relationship between mask 23and diaphragm plate 2i, the intensity of the projected image bearingbeam will always be of a. fixed, predetermined or standard value whenpointer l9 registers with the zero point of dial 18', thereby reducingto a minimum the human-error-element heretofore encountered inphotographic printing.

The device disclosed in Fig. 3 accomplishes substantially the sameresult'as that of the device of Fig. l, but in a somewhat differentmanner. A light sensitive cell H7 is provided interiorly of housing land is wired by means of conductors Md and I to a suitable currentmeasuring instrument or meter H8. The intensity of the modified lightwithin housing will cause pointer H9 to be deflected a definite amount,thereby establishing a readingon meter dial 42 which corresponds to, andis an indication of, the relative intensity of light actually existingwithin said housing.

Coordinated with the calibrations of meter dial 42 is a diaphragm dial43, as shown.

A diaphragmplate 2| i fixedly secured to rock shaft I22 which in turn iscarried by and secured for rotation about its longitudinal axis bybearings I29. Shaft H2 is operatively connected to pointer M which isadapted to sweep diaphragm dial 43 in fixed synchronization with themovement of diaphragm plate 2| relative to projection lens ll. Motionmay be imparted to rock shaft I22 by any suitable means, such as ahandle 28, or the like, whereby the diaphragm dial pointer 44 may becaused to sweep dial 43, under the control of an operator.

In order to standardize the intensity of the projection beam it is onlynecessary for an operator to set the diaphragm pointer 44 to the readingon the diaphragm dial M which corresponds to the reading of the meterpointer on meter dial 42. Diaphragm 2| is operatively connected relativeto pointer 44, and aperture 55 is so proportioned as to alter the sizeof the efiective aperture of lens ll in an inverse ratio to the amountof light in housing if, as indicated on meter 8.

It should be observed that by reason of the V-shape of the aperture 45of the diaphragm plate, it is possible to obtain an infinite number ofefiective projection lens aperture sizes between maximum and minimumlimits, whereby the accuracy of control of the intensity of theprojected beam is at a maximum.

With reference to Figs. 4 and 5 the principle of light control is shownapplied to a so-called photo exposure meter, denoted generally by thenumeral 50. In its most elementary .form such a meter comprises meanssensitive to light, such as, by way of example, a photoelectric cell 51,or the like, and means for indicating potential changes occurring insaid cell, such as a milliainmeter 52, or the like. Cell bi may beelectrically connected to meter 52 by means of conductor be and as.Light-intensity-induced potential changes are visually indicated by theswing of pointer oi meter 52.

The light intensity as indicated byspointer 55 is used as a guide insetting such variable factors in photography, as lens aperture size andshutter speed for given light conditions. However, because of othervariable factors such as iilm speed, etc, it has heretofore been aconfusing and rather I complicated procedurc'to properly coordinate allof the variable factors entering into the final determination of theproper shutter speed for a given lens aperture, and vice versa.

The purpose of the device disclosed in Figs, 4 and 5 is to provide aphoto exposure meter of the type wherein means are provided to simulate,at the light sensitive surface of the cell, certain light conditions forthe purpose of comparing the actual light condition being measuredrelative to a predetermined zero setting, as hereinafter more fullyexplained.

With reference to Fig. 4 it will be noted that there are four variablefactors to beconsidered when using a photo exposure meter, viz. theintensity of light, as indicated by pointer .55; the speed of theparticular film being used, as indicated on chart 56; the shutter speed,as indicated on dial El; and the lens aperture size, as indicated ondial 58.

- Of these four variable factors, two are reduced to constants by theoperator, leaving but two variables to be considered for any given lightcondition.

Inasmuch as the film speed, which is determined by the manufacturer, isconstant for each particular film this variable factor may, for theparticular film being used, be considered as a constant.

The second variable factor which is assumed or considered as beingconstant is either the shutter speed, or the lens aperture setting. Thetwo variable factors remaining then become, first, the intensity oflight, and secondly, either the lens aperture setting or the shutterspeed depending upon which is considered a constant.

For the purpose of illustration it will be assumed that the film speedis 100 and that a shutter speed of second has been selected whereby thelens aperture setting will become a variable function of the intensityof the light. Dial 51 is rotated until the film speed index arrow isaligned with the proper film speed calibration, here 100. The secondcalibration on dial 51 then becomes a constant relative to which thelens aperture settings of dial 58 are taken,

Having thus established the film speed and shutter speed as constantsitis now only necessary to calibrate the lens aperture reading relative tothe preselected shutter speed setting, here second, for the particularlight condition existing at the subject to be photographed. In order toeliminate the necessity for reading complicated calibrations on themeter dial, only one mark, a zero point, is established thereon, andmeans are provided for obtaining a zero point reading of pointer 55 whena predetermined amount of light is permitted to illuminate the activelight sensitive surface of cell 5|.

phragm 59, the outer ring of which is providedv with gear teeth 60engageable by the teeth of gear 6| which is carried by control shaft 62.one end of shaft 62 may terminate in a bearing provided in housing orcase 63 as at 64, while the opposite end thereof may terminate incontrol knob 65, as shown. Knob 85 and the lens aperture dial 58 may beintegral whereby to rotate in unison.

From the foregoing it is apparent that the actual amount of lightreaching the active surface of cell is dependent upon, and is a functionof, the aperture size of iris diaphragm 59. It is likewise apparent thatas the size of the iris diaphragm aperture is varied, for a given sourceof light, pointer 55 will assume various positions between certainmaximum and minimum limits, indicating that greater or lesser amounts ofthe active surface of the cell are being exposed to the source of light.

In order to determine the proper lens aperture for a givenlightcondition with, by way of example, a film speed of 100 and ashutter speed offs second, it is only necessary for an operator to somanipulate knob 65 as to establish the effective aperture of the irisdiaphragm at the active surface of cell 5| at such a setting as topermit just enough light to energize said light sensitive cell as tocause pointer 55 to point to the predetermined zero point. Inasmuch asthe lens aperture dial it is integral with control knob 55, it will beturned with said knob for aligning the proper lens aperture calibrationrelative to the preselected shutter speed calibration, viz. 6 of asecond. As illustrated in Fig. 4 such an aperture setting is 3.5 for theparticular light condition then existing. In the event that theintensity of the light should become less, the pointer would come torest at a value to the left of the zero point, thereby informingtheoperator that for the given film and shutter speeds, the lensaperture setting is too small for the new light condition. In order tobring pointer 55 back to the zero setting, knob 65 is turned to increasethe aperture opening of iris diaphragm 59 thereby allowing more light tofall upon the active surface of cell 5i. As the iris diaphragm is thusbeing adjusted, dial 51 is being simultaneously turned counterclockwiserelative to dial 58 so that as the light meter pointer 55 is returned tozero, a new lens aperture size will be indicated on dial 51 opposite the6 second calibration on dial 58. Obviously the aperture size thusindicated will be greater than the one originally called for when thelight intensity of the subject to be photographed was greater.

It should be understood that, if desired, the shutter speed dial 5? maybe operatively secured to shaft 62 in lieu of the lens aperture dial 58,thereby synchronizing the shutter speed readings relative to theeffective iris diaphragm opening of cell 5|.

It should likewise be understood that various modifications and changesin the structural details of the devices disclosed herein, may be made,withinthe scope of the appended claims, without departing from thespirit of the invention. The present invention is not directed to, norconcerned with, any particular type or kind of light sensitive cell,wherefore any light sensitive cell, regardless of whether it generatesits own potential or requires the use of a battery, may be employed.

It should be understood that in all instances thevarious dials of Figs.4 and 5 are suitably calibrated for effecting properly coordinatedreadings when pointer 55 is returned to the zero point. Likewise therelative motion be ween mask 23 and diaphragmv 20 of Figs. 1 and is socoordinated as to alter the effective aperture size of lens ll inverselyto the light intensity within housing l5.

It should further be observed that mask 23 of Figs. 1 and 2 correspondto and function in a manner similar to the iris diaphragm 59 of Fig. 5;that diaphragm 20 of Figs. 1 and 2 is synchronized relative to cell H ina manner similar to the synchronization between dial 5'! and cell 59 ofFig. 5; and that the setting of diaphragm 2| relative to lens I4 issimilar to the setting of the shutter speed dial 5] relative to the lensaperture dial 58.

It should be observed that the intensity of light within housing I5 isdetermined by, and is a function of, the normal or average density of anegative mounted in gate l3. Therefore, it may be said that the activesurface of a light sensitive cell disposed interiorly of housing IE willreceive and be energized by the total reflected light from the entirenegative, or other light modifying means mounted in gate l3.

It should likewise be noted that by reason of the unique means hereindisclosed for coordinating the setting of diaphragm 2| relative to theparticular total intensity existing within housing IE it is possible toaccurately standardize the intensity of the projected beam whereby theintensity of the projected beam at the printing paper II will always beconstant. The same control means may be used to standardize, prior toprojection, the intensity of the projected beam from flood and spotlight, and the like, in the theatrical, cinema and other fields.

In order to assure constant beam intensity during the projection of aparticular negative, suitable friction means may be provided forprecluding accidental or unintentional movement of diaphragm 2| from agiven setting. If desired, such means may assume the form of a clutch 45wherein a movable plate 46 is secured to and carried by one end of shaft22 or I22 in such a manner as to frictionally engage a fixed plate 8'!which is carried by and secured to the bed frame 48, as shown.

What is claimed is:

1. In a photographic printer, a film support, a paper support, anilluminator disposed at" one side of the film support for projecting abeam of light through a film negative mounted in said film support ontopaper mounted in the paper support, an objective lens spaced from thefilm support, a housing extending between the film support and lens forconfining the image bearing beam, 2. gauge, a light sensitive cellpermanently mounted interiorly of said housing with its light sensitiveelement normally exposed to the reflected light of the image bearingprojected beam as it passes through said housing, said gauge beingdisposed exteriorly of said housing for indicating the potential changesoccurring in said cell in accordance to the light variations occurringwithin said housing, means disposed between the lens and paper supportfor varying the intensity of the projected beam after leaving said lens,said means comprising an opaque plate movable relative to said lens,said plate including an elongated slot having progressively convergentsides each at an equal distance from the axis of said lens wherebymovement of said plate in one direction constricts the lens aperture toprogressively, greater derees and movement in the opposite directionprogressively reduces the constriction of the lens aperture, and meansfor coordinating said last mentioned -m'eans with the gauge readings toadapt the projected imag'e bearing beam to a predetermined intensity. r

2. In a photographic device, the combination of a light cone, a lightsensitive cell fixedly mounted 'interiorly of said cone, an electricalgauge mounted exteriorly of said cone and operatively connected to saidcell, said gauge including a pointer the swing of which is proportionalto the quantity of light energizing said cell, a lens for said lightcone, and means for controlling the effective aperture of said lens inaccordance to the intensity of the light conditions interiorly of saidcone, said means including an opaque plate movable across the axis,

of said lens, said plate provided with a slot having progressivelyconvergent sides each at an equal distance from the axis of the lens, acalibrated lens aperture gauge including a pointer the deflection ofwhich is a, function of the amount by which the aperture of said lens isconstricted by said plate, and means operatively interconnectin saidplate with said last mentioned pointer whereby the lens apertur may bevaried in accordance with and as a predetermined function of thequantity of light energizing said light sensitive cell by correlatingthe setting pointer of the lens aperture gauge with the indication ofthe pointer of said electrical gauge.

3. In a photographic device, the combination of a. light cone, a lightsensitive cell fixedly mounted interiorly of said cone, an electricalgauge mounted exteriorly of said cone and open atively connected to saidcell, said gauge inlight conditions interiorly of said cone, acalibrated lens aperture gauge including a pointer the deflection ofwhich is a function of the amount by which the aperture of saidlens isconstricted by said aperture controlling means. and means operativelyinterconnecting said la t mentioned means with said last mentionedpointer whereby the lens aperture may be varied in accordance with andas a predetermined function of the quantity of light energizing saidlightsensitive cell by correlating the setting pointer of the lensaperture gauge with-the indication of the pointer of said electricalgauge.

4. In a photograph printer, the combination of a light confining housingincluding a light source, an objective lens, and a fixed holder forphotographic negatives, a light sensitive cell ar ranged within thehousing for energizationby light rays from a beam projected through thenegative and toward said lens, an electrical gauge including anindicator observable exteriorly of the housing, said gauge beingelectrically connected with said cell to indicate varying potentialssuch as may occur in the cell by passing the light beam throughnegatives of varying densities, a constant speed shutter in the path ofthe projected beam, manually operated means for controlling theeffective aperture of the lens in accordance with the intensity of lightconditions within the housing as indicated by the electricalgauge, alens aperture gauge including an indicator defiectable in correspondencywith variations in size of the effective lens aperture as established bythe aperture control-- ling means aforesaid, and means operativelyinterconnecting said manually operative aperture controlling means withthe defiectable indicator of the lens aperture gauge, whereby uponcorrelating the lens aperture indicator with the position assumed by theindicator of the electrical gauge, the aperture controlling means willbe automatically adjusted to the value of the light intensity within thehousing.

ALVIN L. MAYER. HANS R. KOSSMAN.

